1. Field of the Invention
This invention relates generally to electronic devices, and more particularly, to interconnect structures for providing electrical conductivity between conductive layers.
2. Discussion of the Related Art
FIGS. 1-6 illustrate the formation of an interconnect for providing electrically conductive connection between conductive layers in accordance with the prior art. Referring to FIG. 1, initially, a conductive, for example metal layer 20 is provided, and a dielectric layer 22, for example silicon dioxide or silicon nitride, is provided on the conductive layer 20. Using well-known photolithographic techniques, a photoresist layer (not shown) is provided on the dielectric layer 22, and is patterned to provide an opening in the photoresist to expose a portion of the dielectric layer 22. Using the remaining photoresist as a mask, an etching step is undertaken, etching away part of the dielectric layer 22 down to the metal layer 20 to provide an opening or passage 24 therethrough to expose a portion of the metal layer 20.
After removal of the photoresist, a Ti/TiN adhesion layer 26 is deposited on the resulting structure, i.e., on the exposed top surface of the dielectric layer 22 and in the opening 24 and on the exposed portion of the metal layer 20 as shown in FIG. 2.
Next, a tungsten nucleation layer 28 is deposited on the entire Ti/TiN adhesion layer 26, the tungsten nucleation layer 28 having a thickness on the order of 50A (FIG. 3). Tungsten 30 is then deposited on the resulting structure, in contact with the tungsten nucleation layer 28 and filling the remaining opening 32 (FIGS. 3 and 4). A chemical-mechanical polish step is undertaken to remove portions of the tungsten 30, tungsten nucleation layer 28, and Ti/TiN adhesion layer 26 down to the top surface of the dielectric layer 22, resulting in the structure shown in FIG. 5, including remaining adhesion layer 26a, tungsten nucleation layer 28a, and tungsten body 30a in the opening. Then, a metal layer 34 is deposited over the resulting structure, in contact with the exposed portion of the material 36 made up of remaining adhesion layer 26a, tungsten nucleation layer 28a, and tungsten body 30a in the opening 24 (FIG. 6). The material 36 in the opening 24 forms an electrically conductive interconnect or plug 38 which provides electrically conductive connection between the conductive metal layer 20 and conductive metal layer 34.
It will be readily understood that it is desirable that the conductive interconnect 38 have very low resistance. The inclusion of a tungsten nucleation layer 28 as described above significantly increases the resistance of the interconnect 38 to electric current traveling between one metal layer and the other. For example, the resistivity of the tungsten nucleation layer is approximately 100 μΩ-cm, and the inclusion thereof greatly increases the overall resistance of the interconnect 38 as compared to pure tungsten.
In addition, there is a continuing trend in electronic devices to decrease device dimensions where possible. In furtherance thereof, the ratio of the length of the conductive interconnect to the cross-sectional width thereof, i.e., the aspect ratio thereof, at approximately 15:1 the in present technology, is expected to increase, i.e., for a given length of conductive interconnect, the cross-sectional width thereof is expected to decrease. This in itself will provide an increase in the resistance of the interconnect.
There is therefore an urgent need to overcome these problems by providing a conductive interconnect or plug with substantially reduced resistance as compared to the prior art. The conductive interconnect should be formed by a simple and cost-effective process and provide high contact integrity.